Single Crystal EPR Studies of [enH₂][{Fe(HEDTA)}₂O]·6H₂O [en = Ethylenediamine; HEDTA = N-Hydroxyethylethylenediaminetriacetate(3−)]

Abstract

Single-crystal EPR studies of the Fe−O−Fe dimer, [enH2][{Fe(HEDTA)}2O]·6H2O, have been performed at both X- and Q-band frequencies and room temperature. Resonances arising from the S‘ = 1, 2, and 3 states have been observed in the powder spectrum at Q-band frequency and analysis by spectral simulation has led to the zero-field splitting parameters: |D 1| = 1.950 cm-1, |E 1| = 0.650 cm-1, |D 2| = 0.150 cm-1, |E 2| = 0.0195 cm-1, |D 3| = 0.570 cm-1, and |E 3| = 0.000 cm-1. In addition, analysis of three orthogonal planes of single-crystal EPR data at both X- and Q-band frequencies has allowed the orientation of the zero-field splitting tensor with respect to the molecular geometry in the dominant (S‘ = 2) state to be determined. The largest principal value of the D tensor (D zz ) is found to lie approximately perpendicular to the plane of the Fe−O−Fe bridge; the nonlinear bridging angle is 165°. The results obtained in this study are compared with those from a number of other studies. A pattern for the orientations of the zero-field splitting parameters in the dominant spin state (S‘ = 2) of the Fe−O−Fe dimers, so far studied by single-crystal EPR spectroscopy, emerges.

On the controversy of metal ion composition on amine oxygenase (AurF): a computational investigation

“…Upon protonation of the m-oxo group, a significant reduction in the J values have been detected (M1p À47.2 cm À1 ; 196 M1p À28.7 cm À1 ). Although the J value has not been reported for this enzyme, the enzyme expressed in overabundance of iron is found to be EPR silent at 15 K. 77 Since no excited state signal has been detected at this temperature, the exchange interaction is likely to be strong 19 and this indirectly indicates that the core has m-O rather than m-OH which is in agreement to the computed J values. For M2 models, a slightly lower estimate of J has been observed compared to the corresponding M1 models (185 cm À1 vs. 133.6 cm À1 for M1 vs. M2).…”

Monoesterase Activity of a Purple Acid Phosphatase Mimic with a Cyclam Platform

“…For coupled-spin systems, which exhibit a distribution of zero-field splitting, the EPR spectra typically arise from an S tot = 3 spin state as the spin projection operators [21] for the other spin states are very large and result in broadening of the resonances. [22][23][24][25][26][27][28] Computer simulations, assuming a strong exchange regime (j J j > j D j) and performed by using the XSophe-Sophe-XeprView computer simulation software suite and an S = 3 effective spin Hamiltonian, incorporating only the zero-field splitting and electron Zeeman interactions (not shown), reproduced some of the resonant field positions and intensities around g eff = 2, but not all and particularly not those at lower magnetic fields. This is not surprising as an examination of the temperature dependence of the resonances around g = 2 (see the Supporting Information) revealed that these resonances arise from transitions within the S tot = 1, 2, and 3 spin states.…”

High-Frequency, High-Field EPR; Magnetic Susceptibility; and X-ray Studies on a Ferromagnetic Heterometallic Complex of Diethanolamine (H2L), [Cu4(NH3)4(HL)4][CdBr4]Br2·3dmf·H2O

“…The orientation and elements of these tensors are not experimentally available, but we may expect that all four tensors are equal except for being oriented differently in space according to the molecular geometry. The zfs tensor for an interaction a−b is likely to be diagonal in a system of coordinates , in that local axis 1 is perpendicular to the plane Cu a −O bridge −Cu b , local axis 2 dissects the Cu a −O bridge −Cu b angle, and axis 3 is perpendicular to both 1 and 2 . Local coordinates for the other three interactions, b−c, c−d, and d−a, are set up in the same way.…”